From Life to Strong Civilization: A Three-Gate Selection Framework for the Parameter Corridor of Civilizational Prospects

How rare is civilization in cosmic parameter space? We decompose the emergence of civilization into a three-step chain of nested questions: (1) under what conditions does a random star–rocky-planet system host *stable life*; (2) given stable life, under what conditions does *civilization* arise; and (3) given civilization, under what conditions does a *strong civilization* able to persist for an Earth-class duration emerge? We model life stability as a five-layer physical filter (star → orbit → body → biology → time window), and model civilization as centennial-scale dynamics of *civilizational order*, scored as the fraction of an observation window during which the civilization survives. Results are obtained from Monte Carlo sampling over N = 50,000 uninformative-prior systems, with an additional 200,000-sample refinement over the golden zone. Three conclusions follow. First, rarity: a random planet produces a strong civilization with probability of only about 0.3% (three per thousand); strong civilization is a rare event in parameter space. Second, a three-driver hierarchy governs civilizational prospects — information carrier (solvent) → planetary core (geologic vitality = magnetic field) → stellar energy flux (temperature) — in decreasing strength, summarized as *"water decides life or death, magnetism decides longevity, energy flux decides lifespan."* Third, a ceiling: carbon-based liquid-water civilizations face an upper civilizational score around 0.6 (Earth's tier sits at ~0.55, the coldest strong line), bounded on one side by the runaway-greenhouse line and on the other by maxed-out phase-transition efficiency. We explicitly separate *direction-locked hard conclusions* from *magnitude-pending open items*, and locate the parameter corridor and golden zone of strong civilization.